Drilling bit for construction work



Nov. 11,' 1958 J. v. EMMONS ETAL 2,859,645

DRILLING BIT FOR CONSTRUCTION WORK Filed April 5, 1957 INVENTORS. JOSEPH V. EMMONS 8 NORMAN A. SMITH BY AT TORNEYS United States Patent DRILLING BIT FOR CONSTRUCTION WORK Joseph V. Emmons, Shaker Heights, and Norman A.

Smith, Cleveland Heights, Ohio, assiguors to The Cleveland Twist Drill Company, Cleveland, Ohio, a corporation of Ohio Application April 5, 1957, Serial No. 650,905

4 Claims. (Cl. 77-70) This invention relates generally as indicated to a drilling bit for construction Work and more particularly to a drilling bit that is especially useful for drilling holes in wood and also in other building materials such as plastics, plaster, fiberboard, and the like, includingincidental. nails, screws, sheet metal, etc., that are apt to be encountered when drilling holes in structural members, walls, partitions, floors, and ceilings of buildings.

The drilling bit constituting the present invention, by reason of its low torque, low thrust characteristics, is ideally suited for manual driving as with a carpenters bit brace and, as well, for power driving. In one case, operator fatigue is reduced and in the other case, power requirements are reduced.

A primary object of this invention is to provide a drilling bit of the character indicated which will not bind, even when drilling a deep hole; which has relatively large flutes for free flow of chips therethrough I so as to avoid necessity of frequent removal of the bit from the hole to clear the chips; which minimizes or eliminates wobbling of the bit as it penetrates the work, thereby avoiding the drilling of bell mouthed, oversize, and rough-walled holes; which requires, as aforesaid, a minimum driving torque to reduce operator fatigue when the bit is hand-driven, or to prevent motor overload when the bit is power-driven; which requires but little axial thrust to penetrate the work; and which is of such construction as to eliminate zones of weakness as caused, for example by termination of the flutes in the shank proper.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawing:

Fig. 1 is a side elevational view of one form of drilling bit made in accordance with the principles of this invention;

Fig. 2 is a side elevational view of the drilling bit illustrated in Fig. 1 taken at right angles to Fig. 1; and

Fig. 3 is an end elevational view on somewhat enlarged scale as viewed from the point or cutting end of Fig. 1.

Referring now in detail to Figs. 1, 2, and 3, the bit there illustrated comprises a shank 1, a shoulder 2, and

- a body 3, the latter terminating in a point or cutting Patented Nov. 11, 1958 vention is concerned, other types of shanks may be employed, for example, straight shanks, tapered shanks, threaded shanks, etc.

The novel features of the present bit reside in the body 3 and the point 4 of said body. The component parts of said body 3, which, together with the point 4 thereof, are of importance herein, are the flutes 5, the lands 6, and the Web 7. These parts, namely, the point 4, the flutes 5, the lands 6, and the web 7, will now be described in detail in the enumerated order.

The point The point or cutting end 4 of the bit comprises two cutting edges or lips 8, the forward end of the web 7 and the clearance or lip relief surfaces 9 the latter, at their intersection, forming a so-called chisel edge 9A. In the present case, the cutting lips 8 form a point angle A of about to 85, the preferred point angle A being about for optimum results.

The forward end of the web 7, at said point 4 has a thickness which is about 8% to about 20% of the diameter of the bit. In the following table the preferred, minimum, and maximum thicknesses of said web 7 at said point 4 are listed for a series of sizes of bits.

Preferred Minimum Maximum Web Web Web Thickness Thickness Thickness Illustrative Bit Diameters at Point (in percent (in percent (in percent of Bit of Bit Diameter) Diameter) Diameter) about 18 about 16 about 20 16 14 18 14 12 16 12 10 l4 l1 9 13 11 9 13 10 8 12 10 8 12 The cutting edges or lips 8 are relieved on the forward end of the lands 6 by the formation of the aforesaid clearance surfaces 9, the lip relief angle B for a series of sizes of bits having preferred, minimum, and maximum angles B as listed in the following table:

Preferred Minimum Maximum Illustrative Bit Diameters Lip Relief Lip Relief Lip Relief Angle (in Angle (m Angle (in degrees) degrees) degrees) about 24 about 21 about 27 In every case, the outside corners 10 of the lips 8 should be at least .010" higher than the rear corners 11.

The flutes The flutes 5, bounded by the helical surfaces of the lands 6, provide helical grooves or channels through which chips are conveyed rearwardly from the cutting end or point 4. The present bit has flutes 5 that are of size adequate for free passage of chips. To further facilitate the flow of chips, the flute surfaces are electropolished so as to have a very low coelficient of friction with the chips, thereby facilitating easy passage of the chips through the flutes 5 toward-the shank end of the bit.

Another noteworthy feature with reference to the flutes 5, is that said flutes 5 terminate in the body 3 of the bit so as to avoid weakening of the shank 1. If desired, said flutes may be extended partway into the shoulder 2 also without creating any region of weakness in the shank]. proper.

The lands The margins 12 of the lands 6 determine the diameter of the body 3 of the bit. Binding of the bit is eliminated by forming the margins 12 of the lands 6 with a back taper of from about .001 to about .004" per inch of length of said body 3, a back taper of about .002" per inch of length of body 3 being preferred. Such back taper provides longitudinal relief for the bit to thus avoid binding in the hole which is being drilled.

In the preferred embodiment of the invention the width of each land 6 is from about 40% to about 50% of the diameter of the bit adjacent to its point 4, such land width being measured along a line which is substantially normal to the outer edges of said lands 6.

The lands 6 additionally are formed with clearances 6A, leaving margins 12 at their leading edges. The margin width should be from about to about 50% of the land width (preferably about 33% of the land width). Lands 6 with margins 12 as specified, serve to materially reduce the friction of the bit against the walls of the hole being drilled, and yet eflectively guide the bit as it is advanced into the work. Such guiding of the bit reduces the tendency to form a bell-mouthed, or over size, or rough-walled hole.

Another feature of the lands 6 which contributes to the superior performance characteristics of the instant bit is that the helix angle D thereof is between about 20 to about a 25 helix angle being preferred.

Such helix angle provides a satisfactory rake angle C for the cutting lips 8 and also provides for desired conveying of chips through the flutes 5. A helix angle D as specified viz. 2030 (25 preferred) further tends to curl the chips in a manner facilitating their easy passage through the flutes 5 without clogging.

The web The web 7 in the bit herein and, in fact, in any drill bit, has the primary function of connecting together the lands 6. The preferred, maximum, and minimum dimensions of the web 7 at point 4- have been listed previously, but as a further feature of this invention, the thickness of said web 7 is progressively increased from the point 4 toward the shank end of body 3. Such increased web "hickness progressively strengthens said body 3 as the I stresses increase, especially during drilling of deep holes. The increase in thickness of said web 7 must be within reasonable limits, since, as evident, an excessive rate of web thickness increase reduces the cross-sectional areas of said flutes 5 to an extent impeding the free flow of chips away from the point 4, with consequent chip clogging and binding of the bit in the hole. It has been found that when the thickness of said web 7 is increased at a rate up to about .012 per inch of length of said body 3, preferably .010" per inch, the required increased strength is provided without constricting the flutes 5 to the extent that chips will clog therein.

If desired, the web 7 at a region substantially removed from the point 4 may beformed with one or more holes 13 for the purpose of fishing wires through drilled holes.

The vastly superior performance of a bit made in accordance with the foregoing specification is specially evident when drilling a hole that has a depth several times the diameter of the bit.

The back-taper of the bit, the clearances 6A of the lands 6, and the helix angle of the lands 6, all mutually contribute, as previously mentioned, in reducing the tendency of binding of the bit when in use. When the bit has the specified land '6 width and Web 7.thickness there is provided ample room in said flutes 5 for facilitat- 4 ing the passage of chips there-through, and furthermore, the chip-clogging tendency is further reduced by electropolishing the walls of said flutes 5. It has been found that electropolished flute walls ofier substantially less resistance to chip flow than do unpolished or mechanically polished walls.

Bit wobble is reduced by reason of the guiding action of the margins 12 of the lands 6 which preferably are about one-third of the specified land width.

A signal feature of the present bit is the reduced torque required to drive it, such reduced torque being achieved by the above described absence of binding and chip clogging, and also, by the construction of said point 4 in accordance with the foregoing specifications insofar as point angle A, web 7 thickness, and lip relief angles B are concerned. These angles A and B and web thickness dimensions regulate the chip thickness so as to keep it within limits for easy turning of the bit.

It has been found also that the specified web thickness and lip relief angles B at the point 4 in cooperation with the specified helix angle result in a moderate desirable tendency for the bit to pull itself into the work without excessive tendency of hogging into the work. These factors also result in a reduction in the required torque and thrust necessary to penetrate the work.

Still another noteworthy feature of this invention is that the flutes 5 terminate in the body 3 (or in the shoulder 2) so as not to create any point of weakness in the shank 1 itself. Such points of weakness have been frequently encountered in the bits of the prior art.

The bit herein described may be made of suitable materials such as are commonly used in the making of wood bits. For instance, carbon tool steels with carbon contents from about 0.60% to about 1.20% have been found well-suited for the present purposes. Alloy steels characterized by the presence therein of useful amounts of alloying elements such as chromium, manganese, tungsten, molybdenum and vanadium may also be used to advantage. When the bit is to be used in the drilling of hard or abrasive materials the cutting end or point 4, may be wholly or partially made of hard metal components, such as tungsten carbide.

Still another feature of the present invention is that no special machines, or special manufacturing techniques need be employed in manufacture, conventional machines and procedures being satisfactory.

When the preferred web thicknesses as previously listed are plotted as the x-ccordinate against the bit diameters as the y-coordinate it will be found that the points be closely on a line that has the following formula:

in which x is the thickness of the web for a bit of diameter y.

Likewise when the preferred lip relief angles are similarly plotted against the bit diameters it will be found that they lie closely on a line that has the following formula: x":26-16y in which at is the lip relief angle for a bit of diameter y.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We therefore, particularly point out and distinctly claim as our invention:

1. A drilling bit adapted for use in the drilling of deep holes in construction materials such as wood and the like and characterized by its low-torque, low-thrust penetraticn of such work; said bit comprising a beck-tapered, helically fluted body that is formed with two helical lands each of Width approximately 40 to of the bit diam eter and each relieved to leave a margin of width approximately 25 to 50% of the land width, such land relief reducing friction of the bit in use and such margins effectively guiding the bit in use to reduce the tendency of forming a bell-mouthed, oversize, or rough-walled hole in the work; a two-lip point of approximately 75 to 85 included angle, the lips of which each have a lip relief angle of approximately 26 minus 16 times the bit diameter; and two helical flutes of approximately 20 to 30 helix angle to provide with said lips a rake angle that eflects moderate pulling in of the bit without hogging into the work and that tends to curl the chips for free passage through said flutes, said flutes leaving therebetween a web that is of thickness at the point of approximately the bit diameter plus .22 divided by 12, whereby said flutes are of relatively large size for free flow of chips therethrough without binding and without requiring periodic bit removal for chip clearing during the drilling of a deep hole in the work.

2. A drilling bit adapted for use in the drilling of deep holes in construction materials such as wood and the like and characterized by its low-torque, low-thrust penetration of such work; said bit comprising a back-tapered, helically fluted body that is formed with two helical lands each of width approximately 40 to 50% of the bit diameter and each relieved to leave a margin of width approximately 33% of the land width, such land relief reducing friction of the bit in use and such margins elfectively guiding the bit in use to reduce the tendency of forming a bell-mouthed, oversize, or rough-walled hole in the work; a two-lip point of approximately 80% included angle, the lips of which each have a lip relief angle of approximately 26 minus 16 times the bit diameter; and two helical flutes of approximately 25 helix angle to provide with said lips a rake angle that eflects moderate pulling in of the bit without hogging into the work and that tends to curl the chips for free passage through said flutes, said flutes leaving therebetween a web that is of thickness at the point of approximately the bit diameter plus .22 divided by 12, whereby said flutes are of relatively large size for free flow of chips therethrough without binding and without requiring periodic bit removal for chip clearing during the drilling of a deep hole in the work.

3. The drilling bit according to claim 2 characterized further in that the web of said body progressively increases in thickness rearward from said point at a rate of about .010 per inch of body length.

4. The drilling bit according to claim 2 characterized further in that said body has a back taper from the point thereof of about .002" per inch of body length to minimize binding of the bit in the work.

References Cited in the file of this patent UNITED STATES PATENTS 2,613,710 Emmons Oct. 14, 1952 FOREIGN PATENTS 563,461 France Sept. 26, 1923 OTHER REFERENCES Suggested Drill Point Angles for Different Materials, American Machinist, page 142, April 12, 1945. 

